1. Field of the Invention
The invention relates to a steering device that is equipped with an electric motor so as to provide steering assist force for the pivoting operation of a steering handle and a control method for the steering device.
2. Description of the Related Art
An electric power steering device according to the related art is equipped with an electric motor so as to provide steering assist force for the pivoting operation of a steering handle, and adjusts the steering assist force by controlling the electrification of the electric motor. Such an electric power steering device is supplied with source power from a vehicle-mounted electric power source device. However, in the case where an abnormality occurs in the vehicle-mounted electric power source device, the electric power steering device cannot appropriately perform the control of the electric motor. Therefore, for example, an electric power steering device proposed in Japanese Patent Application Publication No. 2003-312510 (JP-A-2003-312510) adopts a construction in which when the power source voltage of the vehicle-mounted electric power supply device declines and reaches a predetermined value which is set as an abnormal value, the motor control output gain gradually decreases from 1 to zero, and an assist command value is multiplied by the reduced gain.
However, the electric power steering device proposed in Japanese Patent Application Publication No. 2003-312510 (JP-A-2003-312510) is constructed so as to gradually decrease the gain by which the assist command value is multiplied, irrespective of operation performed by a driver of the vehicle. Therefore, the gain declines even when the driver is not performing a steering operation. Therefore, there occurs a case where when the driver actually performs steering operation, the gain has considerably decreased as compared with the gain obtained at the time of the immediately previous steering operation. In such a case, the steering feel suddenly changes, causing considerable discomfort to the driver.